Oxymonads – eukaryotes without mitochondrion

Mitochondrion is a key evolutionary inventions specific to the eukaryotic cell. Oxymonads remained as one of a few eukaryotic groups, where no mitochondrion has been revealed so far. We have performed detailed genomic and transcriptomic study of oxymonad Monocercomonoides sp., which demonstrates the absence of mitochondrial hallmark proteins. The most striking is the absence of canonical mitochondrial protein import machinery and the substitution of mitochondrial iron sulphur cluster biosynthetic pathway (ISC) by the sulphur mobilization system (SUF). We conclude that Monocercomonoides represents the first report of amitochondriate eukaryote demonstrating the fact that under some circumstances eukaryotes may entirely loose mitochondrion.